Cryptology ePrint Archive: Report 2012/052

Identity-based Encryption with Efficient Revocation

Alexandra Boldyreva and Vipul Goyal and Virendra Kumar

Abstract: Identity-based encryption (IBE) is an exciting
alternative to public-key encryption, as IBE eliminates the need for
a Public Key Infrastructure (PKI). Any setting,
PKI- or identity-based, must provide a means to revoke users from
the system. Efficient revocation is a well-studied problem in the
traditional PKI setting. However in the setting of IBE, there has
been little work on studying the revocation mechanisms. The most
practical solution requires the senders to also use time periods
when encrypting, and all the receivers (regardless of whether their
keys have been compromised or not) to update their private keys
regularly by contacting the trusted authority. We note that this
solution does not scale well -- as the number of users increases,
the work on key updates becomes a bottleneck. We propose an IBE
scheme that significantly improves key-update efficiency on the side
of the trusted party (from linear to logarithmic in the number of
users), while staying efficient for the users. Our scheme builds on
the ideas of the Fuzzy IBE primitive and binary tree data structure,
and is provably secure.